A high speed shared packet channel is known in which, in a downlink of a mobile communication system, a radio base station Node B is configured to perform a scheduling process, an adaptive modulation and coding process, and a HARQ (hybrid ARQ (Auto Repeat reQuest)) retransmission control process.
For example, in the 3GPP, the “HSDPA (High Speed Downlink Packet Access)” is standardized as a mobile communication system using such a high speed shared packet channel.
FIG. 1 is a diagram showing a connection configuration of channels in a mobile communication system using the HSDPA.
A high speed downlink shared channel (HS-DSCH) is a shared channel used for transmitting user data in a downlink of a mobile communication system to which the HSDPA is applied.
An associated dedicated physical channel (A-DPCH) is a dedicated channel associated with the high speed downlink shared channel (HS-DSCH). An associated dedicated physical channel (A-DPCH) for an uplink and the associated dedicated physical channel (A-DPCH) for a downlink form a pair.
The associated dedicated physical channel (A-DPCH) for downlink is configured to transmit transmission power control information (TPC command) on a downlink for controlling a transmission power for an uplink, a layer 3 control signal from a radio network controller RNC, and the like.
The associated dedicated physical channel (A-DPCH) for uplink is configured to transmit user data, a layer 3 control signal to the radio network controller RNC, and the like.
A high speed dedicated physical control channel (HS-DPCCH) is a dedicated physical channel which is used for transmitting a transmission acknowledgement signal (Ack/Nack) of the high speed downlink shared channel (HS-DSCH) and a downlink channel quality indicator (CQI) in an uplink.
The high speed dedicated physical control channel (HS-DPCCH) has a predetermined transmission power offset relative to the associated dedicated physical channel (A-DPCH) for an uplink. In addition, a closed loop transmission power control process is performed on the associated dedicated physical channel (A-DPCH) for an uplink to secure a predetermined receiving quality at a radio base station Node B.
Unlike a mobile communication system of the conventional CDMA system, a hard handover process is performed on the high speed downlink shared channel (HS-DSCH) used in the HSDPA. In contrast, a soft handover process can be performed on the associated dedicated physical channel (A-DPCH) which is transmitted/received in association to the high speed downlink shared channel (HS-DSCH).
In the soft handover process, when performing a transmission power control in an uplink, a mobile station may sometimes receive different transmission power control information (TPC commands) from different cells in a downlink. Since it is sufficient that each channel satisfy a required receiving quality at any one of the cells, the mobile station is configured to decrease the transmission power when at least one of two or more of the received transmission power control information (TPC commands) has a “command (Down command) indicating that the transmission power is to be decreased”.
In a mobile communication system of the CDMA system, there is a problem in general that, unless the soft handover process is performed in an uplink, an interference power from an adjacent cell becomes large that the communication capacity for the uplink is reduced.
FIG. 2 is a diagram showing an example of a mobile communication system employing the HSDPA on which a soft handover process is performed, on an associated dedicated physical channel (A-DPCH).
As shown in FIG. 2, the mobile station UE transmits a high speed dedicated physical control channel (HS-DPCCH) in an uplink, so that the communication quality in a downlink, a transmission acknowledgement signal of the HARQ, and the like are transmitted.
Here, the high speed dedicated physical control channel (HS-DPCCH) has a transmission power offset (gain factor) relative to the dedicated physical control channel (DPCCH) which is one kind of the associated dedicated physical channel (A-DPCH).
In addition, a selective combining is performed on the associated dedicated physical channel (A-DPCH), on which a soft handover process is performed, in a radio network controller RNC. Here, an important factor is the communication quality of a dedicated physical control channel (DPCCH) in an uplink.
To be more precise, in FIG. 1, a transmission power control process is performed on the associated dedicated physical channel (A-DPCH) so that the receiving quality of a cell #1 would be constant. Accordingly, a receiving quality in the cell #1 can also be maintained fixed on the high speed dedicated physical control channel (HS-DPCCH) transmitted with a transmission power obtained by adding a fixed transmission power offset to the transmission power of associated dedicated physical channel (A-DPCH).
However, the receiving quality of the associated dedicated physical channel (A-DPCH) in the cell #1 is lower when the soft handover process is performed than when the soft handover process is not performed. This is because the transmission power control process of the Associated Dedicated Physical Channel (A-DPCH) is performed, at a time when the soft handover is performed, so that the receiving quality of a channel on which a selective combining is performed in the radio network controller RNC becomes constant. In addition, since the associated dedicated physical channel (A-DPCH) does not only follow the receiving quality in the cell #1, the receiving quality of the high speed dedicated physical control channel (HS-DPCCH) in the cell #1 varies with time.
Accordingly, the conventional mobile communication system is normally configured to transmit a high speed dedicated physical control channel (HS-DPCCH) with a larger transmission power offset added thereto when a soft handover process is performed than when a soft handover process is not performed.
However, sometimes it is not realistic to instantaneously increase a transmission power, from the aspect of cost and size, since the performance of a power amplifier of a mobile station UE needs to be enhanced. In such a case, a method is employed where a constant communication quality is satisfied in the high speed dedicated physical control channel (HS-DPCCH), by repeatedly transmitting transmission acknowledgement signals (Ack/Nack) or CQI.
However, there has been a problem that, with such a method, a communication capacity of an uplink is greatly affected by increasing the transmission power of the high speed dedicated physical control channel (HS-DPCCH) and transmitting the high speed dedicated physical control channel (HS-DPCCH) for a long period of time.
Further, there has been a problem that, while repetitive transmission is performed in the high speed dedicated physical control channel (HS-DPCCH), a downlink is not capable of receiving new data during the repetitive transmission, so that the maximum user throughput largely drops in the downlink.
Still further, there has been a problem that, in the case where a closed loop transmission diversity is applied to a channel of a downlink, deterioration in the receiving quality of the Feed Back Information (FBI) in an uplink prohibits a gain of a transmission diversity from being acquired and increases the probability of error in antenna verification, thereby decreasing the throughput of a downlink.
Meanwhile, with regard to an uplink, in the “3GPP” and the “3GPP2” which are international standardizations for the third generation communication system, a method of controlling high-speed radio resources of layer 1 and MAC sub-layer (layer 2) between a radio base station Node B and a mobile station UE have been studied. Such a study or function having been studied are, hereinafter, collectively referred to as an “Enhanced Uplink (EUL)”.
In the Enhanced Uplink, in lower layers (layer 1 and layer 2), each cell of a radio base station Node B controls the transmission rate of a channel to be used for communication in an uplink at a high speed, so that the throughput of each cell can be increased.
To be more precise, as shown in FIG. 3, each cell of the radio base station Node B is configured to measure a “noise rise” of a channel used for communication in an uplink, and to sequentially control the transmission rate of the channel so that the noise rise of the channel converges on a level close to the maximum allowable noise rise.
Here, the noise rise is a ratio between an interference power of a predetermined channel in a predetermined frequency and a noise power (a thermal noise power or a noise power from outside the mobile communication system) in the predetermined frequency. In other words, the noise rise is an offset that a receiving level in a communication state holds compared to a receiving level (noise floor) in a non-communication state.
Incidentally, in the present application, a channel to which the Enhanced Uplink is applied is referred to as an enhanced channel (for example, a dedicated channel to which the Enhanced Uplink is applied is referred to as an “enhanced dedicated channel”).
Also in a mobile communication system to which the Enhanced Uplink is applied, a serving cell (uplink serving cell) mainly performing a scheduling process, a transmission rate control process and the like, is defined. In addition, the uplink serving cell transmits an instruction (Rate Grant) to a serving mobile station UE so as to control the transmission rate
A serving cell of the HSDPA and a serving cell of the Enhanced Uplink are normally set to be the same cell. FIG. 4 is a diagram showing a channel connection configuration of a mobile communication system to which the HSDPA and the Enhanced Uplink are applied.
The enhanced dedicated physical control channel (E-DPCCH) transmits control data for EUL such as: transmission format numbers for determining transmission formats (transmission block size and the like) of E-DPDCH; information on HARQ (the number of retransmissions and the like); and information on scheduling (a transmission power of a mobile station UE, buffer retention amount and the like).
The enhanced dedicated physical data channel (E-DPDCH) is associated with the enhanced dedicated physical control channel (E-DPCCH), and transmits user data for a mobile station UE on the basis of control data for EUL which are transmitted on the enhanced dedicated physical control channel (E-DPCCH).
In the example of FIG. 4, unlike the case where the HSDPA is independently used, the associated dedicated physical channel (A-DPCH) does not need to transmit user data, and may only be configured to transmit control information such as pilot symbols, TPC commands and the like.    [Non-Patent Document 1] “W-CDMA Mobile Communication System”, edited by Keiji Tachikawa, Maruzen Co., Ltd.    [Non-Patent Document 2] 3GPP TR25.896 v6.0.0